so this is my first time posting a question here so please bear with me. I am studying computer science for my bachelors, and I would like some help. We have created various Classes that are all part of a Roster Management System. I have all the classes set up and such, and I can figure out how to store everything in a dynamically allocated array later on, for the time being I am having a difficult time just reading the data needed from a file.
The format for the text file is as follows:
course1-name | course1-code | number-credits | professor-name
student1 first name | student1 last name|credits|gpa|mm/dd/yyyy|mm/dd/yyyy
student2 first name | student2 last name|credits|gpa|mm/dd/yyyy|mm/dd/yyyy
end_roster|
course2-name | course2-code | number-credits | professor-name
student1 first name | student1 last name|credits|gpa|mm/dd/yyyy|mm/dd/yyyy
end_roster|
As you can see, the rosters only have four data fields, course name, course code, number of credits and the professors name.
Students have 6 fields, 7 if you include the end_roster marker (the end_roster marker is literally just that, not a bool value or anything.
Anyway, I cant seem to figure out how to read this input properly. I can read it all in and tokenize it, but then I don't know how to append each "section" to its correct class. This happens to give me each "token" (not 100% clear what that is, but it seems to append each set of characters into a string). I do not know how to assign it into their proper places from this point forward though.
ifstream myroster("rosters.txt");
while( ! myroster.eof() )
{
getline(myroster, line);
cout << line << endl << endl;
char c[line.length() + 1];
strcpy (c, line.c_str());
char * p = strtok(c, "|");
while (p != 0)
{
cout << p << endl;
p = strtok(NULL, "|");
counter++;
}
}
myroster.close();
I've also tried the following;
ifstream myroster("rosters.txt");
while (!myroster.eof())
{
getline(myroster, line, '|');
counter++;
}
Both methods had some form of counter implementation (my first attempt). For example; if counter == 4 it'll be appended to roster, or counter == 6 and its students, but nothing worked (I realized the flaw later on)
The reason I don't just hardcode the program to implement line one for roster1 information, line 2 for student 1, line 3 for student 2, and etc is because the data needs to be edited in the program, and one of the options is to add students/remove them and add rosters/remove them, after which the file needs to be updated again, and then read in again after.
Can anyone shed some light on this?
Related
For my university class in programming we have been working on Object Oriented Programming (OOP) and are currently working on a group project. The project is to create a cash register that holds items with their names, amounts, and prices. As well as have a way to track the coins given by the user then determine the coin denomination. These are supposed to be done in different classes and involve objects.
My question is regarding the inventory manager that I am coding. The inventory manager is supposed to take the "data.txt" file and read it into the appropriate vectors. Currently I have a vector for the item name, price, amount, and then the itemList vector which holds a string of all 3 to print to the user for readability.
Here is a snippet from the data file:
20 1.99 Potato Chips
10 5.99 Ibuprofen
4 1.42 Candy
55 3.10 Coffee
12 3.25 Hummus
12 4.55 Guacamole
7 0.80 Baklava
45 1.50 Chocolate Chip Cookies
My question is, how do I split the line up so that I can pass the amount (first number) to the appropriate vector, pass the price to the appropriate vector, then pass the name to the appropriate vector. Essentially splitting each line into 3 parts. The part that is the most difficult to me is how the names of the items can be 1 word, 2 words, or even 3 words. Making it difficult to predict how many spaces the name will have, which caused a lot of my attempts to not work.
I found a working solution though I'm worried it's incorrect or inefficient and I'm curious in knowing the best way to do this. Thank you so much ahead of time and I will post the class definition and the method I'm working in down below.
< The stream object is inFile>
class inventoryManager
{
private:
double total, change, choice;
vector <int> amount;
vector <string> name;
vector <double> price;
vector <string> itemList;
public:
void fileOpen(fstream& inFile);
void fillInventory(fstream& inFile);
void printInventory(fstream& inFile);
};
void inventoryManager::fillInventory(fstream& inFile)
{
string temp;
string a, b;
while (!inFile.eof())
{
inFile >> a >> b;
amount.push_back(stoi(a));
price.push_back(stod(b));
getline(inFile, temp);
name.push_back(temp);
itemList.push_back(temp);
}
}
Attempted: I tried using the find() function to find each space then use the index to print the estimated indices to each side of the white space to the vectors. Though it was extremely messy and wouldn't work if a different data file was inputted. The idea of the program is to be able to work if a different file is put in, similar format but the amount could be 100, and prices could be more digits. I also tried editing the file directly by adding new lines for each space but ran into the item names with multiple spaces and ultimately didn't work.
You are trying to do too many new things at once. Break the problem into pieces and solve them separately, then combine them. To break the string into pieces you can use find and substr, you just have to be careful and debug until you're sure it's working perfectly:
string s = "45 1.50 Chocolate Chip Cookies";
cout << "s: " << s << endl; // for debugging
size_t first = s.find(' ');
cout << first << endl; // for debugging
string amountString = s.substr(0, first);
cout << amountString << "X" << endl; // for debugging
size_t second = s.find(' ', first+1);
cout << second << endl; // for debugging
string priceString = s.substr(first+1,second-first-1);
cout << priceString << "X" << endl; // for debugging
string nameString = s.substr(second+1);
cout << nameString << "X" << endl; // for debugging
The purpose of those X's is to be certain that the substring has no trailing space.
Once you have tackled the problem this way (and handed the result in for a grade), you can advance to tools like stringstream, and you won't have to deal with this grubby index arithmetic any more.
I'm trying to get my program to read two lines out of a six line data file (the other four are two sets of two that are meant to be read to other objects). However, I can only get it to read one -- either the first or the second depending on how I manipulate the code.
Here's what's in my data file:
Mustang Sally
123.45
George Porge
11.99
J. D. Rockerfeller
56321.3
And here's the section of the code where I need to read said data:
void account::readAccount(ifstream &inFile)
{
while (getline(inFile, name))
{
inFile.ignore();
inFile >> savings;
}
}
The code above is only reading in the second line.
I think I'm having a phantom newline problem, which I can't seem to resolve, but I also feel that there's another problem on top of that, which I can't comprehend with my current level of experience regarding file streams.
The code above is only reading in the second line.
Yes because you tell it to ignore. I don't know what exactly two lines you want to get from these, but based on the codes, I'm assuming that you want to read the values at line 2,4. The following code will print out those two lines.
float savings = 0.0f;
while(getline(inFile,line))
{
if(savings > 0.0f) cout << savings << endl;
inFile >> savings;
inFile.ignore(1000, '\n' );
}
I wanted to ask how can I append strings to the end of fixed number of lines (fixed position). I am trying and searching books and websites for my answer but I couldn't find what I am doing wrong.
My structure :
const int numberofdays=150 ;
const int numberofstudents=2;
struct students
{
char attendance[numberofdays]; int rollno;
char fullname[50],fathersname[50];
}
Creating a text file
ofstream datafile("data.txt", ios::out );
Then I take input from the user and save it to the file.
How I save my data to text files :
datafile <<attendance <<endl<< rollno <<endl<<
fullname <<endl<< fathersname <<endl ;
How it looks like in text files :
p // p for present - 1st line
1 // roll number
Monte Cristo // full name
Black Michael // Fathers name
a // a for absent - 5th line
2 // roll number
Johnson // full name
Nikolas // Fathers name
How I try to update the file. (updating attendance for everyday)
datafile.open("data.txt", ios::ate | ios::out | ios::in);
if (!datafile)
{
cerr <<"File couldn't be opened";
exit (1);
}
for (int i=1 ; i<=numberofstudents ; i++)
{
long int offset = ( (i-1) * sizeof(students) );
system("cls");
cout <<"\t\tPresent : p \n\t\t Absent : a"<<endl;
cout <<"\nRoll #"<<i<<" : ";
cin >> ch1;
if (ch1 != 'p')
ch1 = 'a';
datafile.seekp(offset);
datafile <<ch1;
datafile.seekg(0);
}
I just want to add (append) characters 'p' or 'a' to the first or fifth line, I tried every possible way but I am unable to do it.
What you are doing is fairly common, but as you say it is inefficient if the size of data grows. Two solutions are to have fixed size records and index files.
For fixed-size records, in the file write the exact bytes of your data structure rather than a variable length text. This would mean you don't have a text file any more, but a binary file. You can then calculate the position to seek to easily.
To create an index file, write two files at once, one your variable size record file, and the other write a binary value with either the offset of the data from the start of the file. Since the index is a fixed size, you can seek to the index, read it, then seek to the position in the data file. If the new record will fit, you can update it in place, otherwise fill in with blanks and put the updated record at the end of the data file, then update the index file to point to the new location. This is basically how early PC databases worked.
Fixed size records are rather inflexible, and by the time you've implemented the index file system and tested it, now-a-days you probably would use a in-process database instead.
I came up with my own (easy & inefficient) logic to copy every line (except the line I want to update) to the another file.
I made my text file to be created like this :
=p // p for present - 1st line
1 // roll number
Monte Cristo // full name
Black Michael // Fathers name
=a // a for absent - 5th line
2 // roll number
Johnson // full name
Nikolas // Fathers name
Then I made the following code to update 1st and 5th line :
ifstream datafile("data.txt", ios ::in);
ofstream tempfile("temp.txt" , ios ::out);
string data, ch1;
while (getline(datafile,data))
{
if (data[0]=='=')
{
system("cls");
cout <<"\t\tPresent : p\n\t\tAbsent : a"<<endl;
cout <<"\nRoll #"<<i<<" : ";
cin >> ch1;
++i;
if (ch1 != "p")
ch1 = "a";
data=data+ch1; // Appending (updating) lines.
}
tempfile <<data <<endl; // If it was 1st or 5th line, it got updated
}
datafile.close(); tempfile.close();
remove("data.txt"); rename("temp.txt" , "data.txt");
But as you can see, this logic is inefficient. I will still wait for someone to inform me if I could somehow move my file pointer to exact location (1st and 5th line) and update them.
Cheers!
i have a text file with data like the following:
name
weight
groupcode
name
weight
groupcode
name
weight
groupcode
now i want write the data of all persons into a output file till the maximum weight of 10000 kg is reached.
currently i have this:
void loadData(){
ifstream readFile( "inFile.txt" );
if( !readFile.is_open() )
{
cout << "Cannot open file" << endl;
}
else
{
cout << "Open file" << endl;
}
char row[30]; // max length of a value
while(readFile.getline (row, 50))
{
cout << row << endl;
// how can i store the data into a list and also calculating the total weight?
}
readFile.close();
}
i work with visual studio 2010 professional!
because i am a c++ beginner there could be is a better way! i am open for any idea's and suggestions
thanks in advance!
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <limits>
struct entry
{
entry()
: weight()
{ }
std::string name;
int weight; // kg
std::string group_code;
};
// content of data.txt
// (without leading space)
//
// John
// 80
// Wrestler
//
// Joe
// 75
// Cowboy
int main()
{
std::ifstream stream("data.txt");
if (stream)
{
std::vector<entry> entries;
const int limit_total_weight = 10000; // kg
int total_weight = 0; // kg
entry current;
while (std::getline(stream, current.name) &&
stream >> current.weight &&
stream.ignore(std::numeric_limits<std::streamsize>::max(), '\n') && // skip the rest of the line containing the weight
std::getline(stream, current.group_code))
{
entries.push_back(current);
total_weight += current.weight;
if (total_weight > limit_total_weight)
{
break;
}
// ignore empty line
stream.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}
else
{
std::cerr << "could not open the file" << std::endl;
}
}
Edit: Since you wannt to write the entries to a file, just stream out the entries instead of storing them in the vector. And of course you could overload the operator >> and operator << for the entry type.
Well here's a clue. Do you see the mismatch between your code and your problem description? In your problem description you have the data in groups of four lines, name, weight, groupcode, and a blank line. But in your code you only read one line each time round your loop, you should read four lines each time round your loop. So something like this
char name[30];
char weight[30];
char groupcode[30];
char blank[30];
while (readFile.getline (name, 30) &&
readFile.getline (weight, 30) &&
readFile.getline (groupcode, 30) &&
readFile.getline (blank, 30))
{
// now do something with name, weight and groupcode
}
Not perfect by a long way, but hopefully will get you started on the right track. Remember the structure of your code should match the structure of your problem description.
Have two file pointers, try reading input file and keep writing to o/p file. Meanwhile have a counter and keep incrementing with weight. When weight >= 10k, break the loop. By then you will have required data in o/p file.
Use this link for list of I/O APIs:
http://msdn.microsoft.com/en-us/library/aa364232(v=VS.85).aspx
If you want to struggle through things to build a working program on your own, read this. If you'd rather learn by example and study a strong example of C++ input/output, I'd definitely suggest poring over Simon's code.
First things first: You created a row buffer with 30 characters when you wrote, "char row[30];"
In the next line, you should change the readFile.getline(row, 50) call to readFile.getline(row, 30). Otherwise, it will try to read in 50 characters, and if someone has a name longer than 30, the memory past the buffer will become corrupted. So, that's a no-no. ;)
If you want to learn C++, I would strongly suggest that you use the standard library for I/O rather than the Microsoft-specific libraries that rplusg suggested. You're on the right track with ifstream and getline. If you want to learn pure C++, Simon has the right idea in his comment about switching out the character array for an std::string.
Anyway, john gave good advice about structuring your program around the problem description. As he said, you will want to read four lines with every iteration of the loop. When you read the weight line, you will want to find a way to get numerical output from it (if you're sticking with the character array, try http://www.cplusplus.com/reference/clibrary/cstdlib/atoi/, or try http://www.cplusplus.com/reference/clibrary/cstdlib/atof/ for non-whole numbers). Then you can add that to a running weight total. Each iteration, output data to a file as required, and once your weight total >= 10000, that's when you know to break out of the loop.
However, you might not want to use getline inside of your while condition at all: Since you have to use getline four times each loop iteration, you would either have to use something similar to Simon's code or store your results in four separate buffers if you did it that way (otherwise, you won't have time to read the weight and print out the line before the next line is read in!).
Instead, you can also structure the loop to be while(total <= 10000) or something similar. In that case, you can use four sets of if(readFile.getline(row, 30)) inside of the loop, and you'll be able to read in the weight and print things out in between each set. The loop will end automatically after the iteration that pushes the total weight over 10000...but you should also break out of it if you reach the end of the file, or you'll be stuck in a loop for all eternity. :p
Good luck!
So I have a binary file that I create and initialize. If I set my pointer to seekg = 0 or seekp = 0, then I can overwrite the line of text fine. However if I jump ahead 26 bytes (the size of one line of my file and something I have certainly confirmed), it refuses to overwrite. Instead it just adds it before the binary data and pushes the old data further onto the line. I want the data completely overwritten.
char space1[2] = { ',' , ' '};
int main()
{
CarHashFile lead;
lead.createFile(8, cout);
fstream in;
char* tempS;
tempS = new char[25];
in.open("CarHash.dat", ios::binary | ios::in | ios::out);
int x = 2000;
for(int i = 0; i < 6; i++)
tempS[i] = 'a';
int T = 30;
in.seekp(26); //Start of second line
in.write(tempS, 6); //Will not delete anything, will push
in.write(space1, sizeof(space1)); //contents back
in.write((char *)(&T), sizeof(T));
in.write(space1, sizeof(space1));
in.write(tempS,6);
in.write(space1, sizeof(space1));
in.write((char *)&x, sizeof(x));
//Now we will use seekp(0) and write to the first line
//it WILL overwrite the first line perfectly fine
in.seekp(0);
in.write(tempS, 6);
in.write((char*) &x, sizeof(x));
in.write(tempS, 6);
in.write((char *) &T, sizeof(T));
return 0;
}
The CarHashFile is an outside class that creates a binary file full of the following contents when create file is invoked: "Free, " 1900 ", Black, $" 0.00f.
Everything enclosed in quotes was added as a string, 1900 as an int, and 0.00f as a float obviously. I added all of these through write, so I'm pretty sure it's an actual binary file, I just don't know why it only chooses to write over the first line. I know the file size is correct because if I set seekp = 26 it will print at the beginning of the second line and push it down. space was created to easily add the ", " combo to the file, there is also a char dol[1] = '$' array for simplicity and a char nl[1] = '\n' that lets me add a new line to the binary file (just tried removing that binary add and it forced everything onto one row, so afaik, its needed).
EDIT: Ok so, it was erasing the line all along, it just wasn't putting in a new line (kind of embarrassing). But now I can't figure out how to insert a newline into the file. I tried writing it the way I originally did with char nl[1] = { '\n' }. That worked when I first created the file, but won't afterwards. Are there any other ways to add lines? I also tried in << endl and got nothing.
I suggest taking this one step at a time. the code looks OK to me, but lack of error checking will mean any behavior could be happening.
Add error checks and reporting to all operations on in.
If that shows no issues, do a simple seek then write
result = in.pseek(26);
//print result
result = in.write("Hello World",10);
// print result
in.close();
lets know what happens
The end problem wasn't my understand of file streams. It was my lack of understanding of binary files. The newline screwed everything up royally, and while it could be added fine at one point in time, dealing with it later was a huge hassle. Once I removed that, everything else fell into place just fine. And the reason a lot of error checking or lack of closing files is there is because its just driver code. Its as bare bones as possible, I really didn't care what happened to the file at that point in time and I knew it was being opened. Why waste my time? The final version has error checks, when the main program was rewritten. And like I said, what I didn't get was binary files, not file streams. So AJ's response wasn't very useful, at all. And I had to have 25 characters as part of the assignment, no name is 25 characters long, so it gets filled up with junk. Its a byproduct of the project, nothing I can do about it, other than try and fill it with spaces, which just takes more time than skipping ahead and writing from there. So I chose to write what would probably be the average name (8 chars) and then just jump ahead 25 afterwards. The only real solution I could say that was given here was from Emile, who told me to get a Hex Editor. THAT really helped. Thanks for your time.